The following principle of ultrasonic diagnostic apparatuses already has been well known: an ultrasonic wave is transmitted to the inside of the body and a reflected wave thereof is received by using a transducer array, whereby two-dimensional information about the interior of the body is obtained.
An ultrasonic diagnostic apparatus that performs sector scanning by using a transducer array is configured as shown in FIG. 4, for example. An operation of the ultrasonic diagnostic apparatus that performs sector scanning will be described with reference to FIG. 4. Transducers 8-1 to 8-8 for transmitting and receiving an ultrasonic wave are connected with transmission pulse generators 9-1 to 9-8, respectively, for generating transmission pulses for driving the transducers 8-1 to 8-8. A transmission trigger generator 10 generates trigger pulses that allow the transmission pulse generators 9-1 to 9-8 to generate the transmission pulses, and a controller 5 controls the transmission trigger generator 10 and a transmission power source 11. The transmission power source 11 supplies the transmission pulse generators 9-1 to 9-8 with a voltage that determines an amplitude of the transmission pulses to be generated by the transmission pulse generators 9-1 to 9-8. An output side capacitor 7 is provided to stabilize a voltage of the transmission power source 11.
Reception amplifiers 12-1 to 12-8 appropriately amplify signals from the transducers 8-1 to 8-8, respectively, that have received a reflected ultrasonic wave. A beam former 13 subjects the amplified signals to delay addition, and a wave detector 14 detects the resulting signals. A scan converter (DSC) 15 subjects the detected signals to scan conversion, and a display 16 displays an image based on the resulting signals.
Recently, a single ultrasonic diagnostic apparatus can accommodate a Doppler mode in which blood flow information is displayed according to a spectrum, a color flow mode in which blood blow information is displayed in colors, as well as a B-mode in which an image is displayed by converting amplitude information into luminance, so as to perform a different mode operation for each scan.
As compared with the B-mode that requires a high resolution, the color flow mode and the Doppler mode require a high sensitivity. Accordingly, for a diagnosis, the wave number of a transmission waveform per pulse in the B-mode often is set lower than that in the color flow mode or the Doppler mode.
There are regulations on the intensity of an ultrasonic wave that can be incident on the inside of the body. In the case of a high wave number, the power per unit time becomes higher even with the same amplitude, and accordingly the amplitude needs to be set lower. On the other hand, in the B-mode in which the wave number is low, the amplitude needs to be increased within a stipulated range so as to increase a S/N ratio.
Consequently, in order to switch mutually between the B-mode, the color flow mode, and the Doppler mode at a high speed, it is necessary to change the output voltage of the transmission power source 11 rapidly. However, in the method as shown in FIG. 4 in which the single transmission power source 11 supplies power to all the transmission pulse generators 9-1 to 9-8, high-speed switching is difficult due to the large amount of power supply.
To solve this problem, for example, Patent Document 1 describes a method in which a plurality of power sources are provided and a power source to supply power is selected by a switch.
FIG. 5A is a block diagram showing a configuration from a transmission power source to transmission pulse generators (not shown) in the ultrasonic diagnostic apparatus described in Patent Document 1. FIG. 5B is a timing chart showing switching of a transmission voltage. This ultrasonic diagnostic apparatus includes mode-specific power sources 1A and 1B for supplying power, a controller 5 for controlling the voltage of the mode-specific power sources 1A and 1B, power source side capacitors 3A and 3B for stabilizing the voltage of the mode-specific power sources 1A and 1B, respectively, a mode changeover switch 18 for switching between the mode-specific power sources 1A and 1B, and an output side capacitor 7. When generating transmission pulses, the transmission pulse generators rapidly consume power, followed by a voltage drop due to an internal resistance of the mode changeover switch 18 not being zero, and the output voltage decreases. The output side capacitor 7 is used as a temporary power source in such a case.
In FIG. 5B, VB represents an output voltage VB shown in FIG. 5A to be supplied to the transmission pulse generators. SW18 represents a connection state of the mode changeover switch 18. Output represents a voltage of transmission pulses for driving a transducer transmitted from the transmission pulse generators. When a transmission waveform with an amplitude V1 is generated to be transmitted to the transducer as Output for the B-mode (before Time t1), the mode changeover switch 18 is connected to an a side, so that a voltage VB1 is supplied from the mode-specific power source 1A. Then, when a transmission waveform with an amplitude V2 lower than the amplitude V1 is generated for the color flow mode (after Time t1), the mode changeover switch 18 is connected to a b side, so that an output voltage VB2 of the mode-specific power source 1B is supplied, and VB becomes equal to VB2. By repeating this operation, transmission and reception for the B-mode and those for the color flow mode are performed in a time-sharing manner.
Patent Document 1: JP 11(1999)-290321 A